Diagnostics of caesium emission from SPIDER caesium oven prototype

The use of caesium vapour is mandatory in plasma sources for negative ion beams to achieve a sufficient negative ion density. In the SPIDER ion source, three caesium ovens will provide a sufficiently high caesium flux to the walls of the ion source, but also a relatively even caesium distribution in the ion source. In order to ensure the caesium ovens are operating properly in terms of repeatability of the evaporated caesium flow, and to characterize the caesium flux emitted from its nozzles, a CAesium Test Stand (CATS) was equipped with a set of diagnostics. This paper reports the present configuration of the diagnostic set-up. Surface ionization probes are installed in front of the nozzle apertures. Movable surface ionization detectors are installed to reconstruct the angular distribution of the emission. A quartz microbalance is installed at a fixed position, to measure the cumulated caesium flux. Finally, the laser absorption spectroscopy measures the line-integrated caesium density. An example of these combined measurements is presented.